We can tune the device to a singlet GS region by making the backgate voltage less negative (see Fig.  REFC around \(V_{\textrm {bg}} = -1.84 \, {V}\) , green dashed square). The excitations from this singlet GS are doublet-like and hence split under a Zeeman field [1]}, as opposed to the previous case. Figure  REFA presents a detailed zoom of device B in this gate region. Fig.  REFB shows the same scan but for \(B = 115\, {mT}\)  (corresponding to the center of the first LP lobe). Since two spin-polarized excitations from the singlet GS are possible [1]}, two pairs of ABSs are observed: one at lower bias and another at higher bias (denoted as \(\zeta _\uparrow \)  and \(\zeta _\downarrow \)  in the sketch of Fig.  REFC). The \(B\) -field evolution at \(V_{\textrm {bg}} = -1.84 \, {V}\)  (dashed line in Fig.  REFA) is displayed in Fig.  REFD. In the zeroth lobe, the pair of ABSs neither splits nor moves. In contrast, the ABSs show a clear Zeeman splitting in the first lobe. For increasing magnetic fields, the lowest ABS excitation moves towards zero energy at the end of the first lobe, forming a ZBP. This zero-energy crossing signals a QPT to a spin polarized doublet GS. The ZBP persists throughout the second lobe, as revealed in Fig.  REFD. Our theoretical analysis of this regime supports this interpretation and explains the absence of a clear Zeeman splitting in the zeroth lobe (see Fig. S3 in the SI).
<FIGURE>